1. Field of the Invention
The present invention relates generally to a wavelength converting device for obtaining, for example, a second order harmonic by converting the wavelength of a light beam such as a laser, and more specifically to a wavelength converting device having a substrate composed of MgO and a waveguide formed of a KNbO.sub.3 membrane and a method of fabricating the wavelength converting device.
2. Description of the Related Art
A wavelength converting device has a function of radiating a second order harmonic of a laser. This is preferably utilized for obtaining a laser having a shorter wavelength. A typical wavelength converting device has: a substrate composed of MgO; a waveguide formed of a KNbO.sub.3 membrane, which is formed on the substrate by crystal growth; an electrode member formed on the surface of the KNbO.sub.3 membrane; and a stripe-shaped TiO.sub.2 membrane which is used to shut the light therein and which is formed on the surface of the KNbO.sub.3 membrane. The KNbO.sub.3 membrane has characteristics that a non-linear optical constant is large and that a light damage resistance is high. Therefore, this type of the wave converting device enables high efficient wavelength conversion and has a long life.
However, this type of wave converting device has a problem that deformation occurs in the KNbO.sub.3 membrane because the lattice constant of the KNbO.sub.3 membrane is mismatched with that of the MgO. This causes a loss to propagation of a light.
Meanwhile, the KNbO.sub.3 membrane is formed on the MgO substrate by inducing crystal growth in fabrication of this wavelength conversion device. In the fabrication process, not only a crystal plane having a necessary crystal orientation ((001) plane) but also a crystal plane having an unnecessary crystal orientation (for example, (011) plane) is grown. As a result, efficiency of the wavelength conversion is undesirably reduced.